1. Field of the Invention
This invention relates in general to electrical submersible well pumps, and in particular to couplings between splined shafts of submersible pumping systems and methods of providing enhanced alignment of motor and driven shafts of submersible pumping systems and electrical submersible pumps.
2. Description of the Related Art
Electrical submersible pumps (ESP) are commonly used for hydrocarbon well production, FIG. 1 provides an example of a submersible pumping system 10 disposed within a wellbore 5. The wellbore 5 is lined with casing 4 and extends into a subterranean formation 6. Perforations 9 extend from within the wellbore 5 through the casing 4 into the formation 6. Hydrocarbon fluid flow, illustrated by the arrows A, exits the perforations 9 into the wellbore 5, where it can either be pumped by the system 10 or migrate to a wellhead 12 disposed on top of the wellbore 5. The wellhead 12 regulates and distributes the hydrocarbon fluid for processing or refining through an associated production line 7.
The pumping system 10 includes an electrical submersible pump (ESP) 14 with production tubing 24 attached to its upper end. The ESP 14 comprises a motor 16, an equalizer or seal 18, a separator 20, and a pump 22. A fluid inlet 26 is formed in the housing in the region of the ESP 14 proximate to the separator section 20. The fluid inlet 26 provides a passage for the produced hydrocarbons within the wellbore 5 to enter the ESP 14 and flow to the pump 22. Fluid pressurized by the pump 22 is conveyed through the production tubing 24 connecting the ESP 14 discharge to the wellhead 12. The pump 22 and separator 20 are powered by the motor 16 via a shaft (not shown) that extends from the motor 16. The shaft is typically coupled to respective shafts in each of the pump 22, separator 20, and seal 14.
Delivering the rotational torque generated by an ESP motor 16 typically involves coupling a motor shaft (i.e., a shaft connected to a motor or power source) to one end of a driven shaft, wherein the other end of the driven shaft is connected to and drives rotating machinery. Examples of rotating machinery include a pump, a separator, and tandem pumps. One type of coupling comprises adding splines on the respective ends of the shafts being coupled and inserting an annular collar over the splined ends, where the annular collar includes corresponding splines on its inner surface. The rotational force is well distributed over the splines, thereby reducing some problems of stress concentrations that may occur with keys, pins, or set screws. Examples of a spline cross-section include an involute and a square tooth. Typically, splines having an involute cross-section are smaller than square tooth splines, thereby leaving more of the functional shaft diameter of a shaft to carry a rotational torque load. Additionally, involute spline shapes force the female spline to center its profile on the male spline, thus coaxially aligning the shafts in the coupling with limited vibration. Square tooth splines are made without specialized cutters on an ordinary mill. However, square teeth spline couplings do not align like involute teeth unless the clearance is reduced or the male and female fittings are forced together. However, reducing clearance or force fitting square teeth splines prevents ready assembly or disassembly.